ANP SECRETION FROM SMALL-CELL LUNG-CANCER CELL-LINES - A POTENTIAL MODEL OF ANP RELEASE

Although atrial distension is widely accepted as the primary stimulus for atrial natriuretic peptide (ANP) release, a number of agonists are also known to induce its secretion. The mechanisms underlying these p rocesses are not well understood. Studies of this nature are hampered by the inherent difficulty in culturing homogeneous populations of car diac myocytes in sufficient quantities to perform molecular investigat ions. For this reason, we have examined the possibility of using other cell types as a model of ANP release. It has been reported that a num ber of tumor samples from small cell lung cancer (SCLC) patients expre ss the ANP gene. Characterization of a large number of cell lines deri ved from SCLC tumor samples indicated that two of these cell lines, OS -A and SHP-77, secrete ANP at rates of similar to 10(-20) g . cell(-1) . min(-1). This is a sufficient quantity to facilitate secretion studi es using a perifusion system. We have demonstrated that ANP is release d through regulated secretory pathways, as the Ca2+ ionophore A-23187, arginine vasopressin (AVP), and the sodium ionophore, monensin, were capable of modifying secretion rates. High-pressure liquid chromatogra phy (HPLC) analysis indicated that the primary secretory product is AN P-(99-126), the circulating form of this hormone. Intracellularly, bot h ANP-(99-126) and ANP-(1-126) were present, suggesting the synthesis and appropriate cleavage of pro-ANP-(1-126). Because both of these cel l lines have doubling times in the range of 3-5 days, they could serve as a rapidly proliferating and easily maintainable supply of homogene ous tissue for release studies. The two identified SCLC cell lines may provide a unique opportunity to investigate the molecular events asso ciated with ANP secretion.